1. Field of the Invention
The present invention relates to an image forming apparatus and the method for controlling the image forming apparatus, in particular, the image forming apparatus using the RAIDs (Redundant Arrays of Inexpensive Disks) and the method for controlling the above image forming apparatus.
2. Description of Related Art
Conventionally, in many cases, a storing device stores data by using one HDD (Hard Disk Drive). However, because the HDD has movable parts, the failure easily occurs in the HDD due to the deterioration of the movable parts or the like. Therefore, when the failure occurs, there is some possibility that all of the stored data are lost. Further, in the HDD, the access speed for accessing data is slow as compared with a semiconductor memory.
In order to safely store data and to read and write data at a high speed, the method called as RAID in which a plurality of HDDs are used, has been proposed. In the RAID, there are a plurality of levels and the effects are different according to the levels. For example, the RAID0 classified as level 0, is the method in which data can be read and written at a high speed by dispersively storing data in a plurality of HDDs. The RAID1 classified as level 1, is the method in which the same data is written in a plurality of HDDs to enhance the fault tolerance. The RAID has been used in a large-scale business server or a workstation which is required to process a large quantity of data at a high speed and to enhance the fault tolerance and in a computing device or the like which is manufactured for a specific purpose. In recent years, the RAID has been used in a multi-function peripheral or the like.
However, in each of the above RAIDs, there are some problems. In the RAID0 (striping), it is possible to read and write the data at a high speed by using the RAID0, however, when one HDD is failed, all of the data cannot be used (that is, the RAID0 has no fault tolerance). In the RAID1 (mirroring), it is possible to enhance the fault tolerance by using the RAID1, however, because the same data is stored in a plurality of HDDs, the redundant data are caused in proportion to the number of HDDs used for the mirroring and the writing speed becomes slow.
Further, various types of data are stored in the storing device. In case of the data which is frequently accessed, it is considered that the reading and writing speed is more important than the fault tolerance. On the other hand, in case of the data that is intended to be stored, it is considered that the fault tolerance is more important than the reading and writing speed. Therefore, in the storing device for storing the data by using the RAID0 or the RAID1, there was a problem in which various types of data cannot be effectively stored.
In order to solve the above problem, the following storing device is proposed. In the storing device, by using a plurality of HDDs in which the RAID can be carried out, it is possible to read and write the data at a high speed and to improve the fault tolerance according to the type of data (See Japanese Patent Application Publication No. 2010-198424).
In the method disclosed in the above Japanese Patent Application Publication, it is possible to read and write the data at a high speed and to improve the fault tolerance according to the type of data. However, in the above publication, it is not specifically disclosed how to cope with the failure of the storing device since the HDD is failed until the failed HDD is replaced. For example, in case that two HDDs are provided, when one HDD is failed, the mirroring cannot be carried out until the failed HDD is replaced with new one. As a result, the fault tolerance is lost. Further, while only one HDD is actuated, it is not possible to carry out the striping. Therefore, it takes a long time to read and write the data as compared with the case in which the striping is carried out by using a plurality of HDDs. Further, in a multi-function peripheral or the like in which the above technology is diverted, the productivity is decreased when the above situation is caused.